This invention relates generally to molded case circuit breakers and more particularly to a line terminal assembly for a circuit breaker.
In a circuit breaker, line current enters through a line terminal assembly which includes a line terminal lug for mechanically fastening the line to the terminal assembly. Electrical current typically travels from the line terminal lug through the line terminal assembly to the circuit breaker contact assembly. It is desirable to cause the circuit breaker to trip in reponse to current flow through the circuit breaker of a certain magnitude to protect the circuit in which it is connected from over current conditions. This function is accomplished in thermal-magnetic circuit breakers by the use of a thermal element in conjunction with a magnetic structure.
In a circuit breaker, it is customary to provide for adjusting the current level at which the circuit breaker will trip. This insures that the circuit breaker will trip at a preselected level above its rated current. Typically, the thermal element is a bimetallic strip which bends when heated in response to the flow of current through it. The bimetallic element operates the trip lever of the circuit breaker which causes the circuit breaker to topen thereby interrupting the flow of current through the circuit breaker when the current flow heats the bimetallic strip. The bimetallic strip is very sensitive, and understandably, adjusting or calibrating the bimetallic strip is a very delicate operation.
Since current flows through the bimetallic strip, it is connected so that current flow from the line terminal flows through the line terminal to the bimetallic strip through the bimetallic strip to the circuit breaker operating contacts. Connection from the bimetallic strip to the contact assembly is conveniently made by way of a flexible connector such as a pigtail connector. Unfortunately, the presence of the pigtail connector can be felt by the bimetallic strip and can interfere with the operation and, more importantly, the calibration of the circuit breaker. Accordingly, it will be appreciated that it would be highly desirable to provide a thermal element for a molded case circuit breaker which is easy to calibrate and is not severely affected by its connection to the contact assembly.
The molded case circuit breaker has a molder case with ribs, grooves or barriers fabricted therein for receiving the components of the line terminal assembly. Circuit breakers are items which are mass produced and are made within certain manufucaturing tolerances; thus, the molded case is made to accomodate all of the expected variances in the components of the line terminal assembly. The net result is that a tight, precision fit of the components in the molded case is not always achieved, which can lead to variations in the tripping current of the circuit breaker. For this reason, calibration of each circuit breaker is necessary. Accordingly, it will be appreciated that it would be highly desirable to provide a circuit breaker which provides a tight fit for the components of the line terminal assembly.
Accordingly, it is an object of the present invention to provide a molded case circuit breaker which has a line terminal assembly which fits tightly in the molded case of the circuit breaker.
Another object of the present invention is to provide a line terminal assembly which has a bimetallic element and can be easily calibrated.